In recent years, in order to reduce environmental stresses, it has been investigated to replace halogen-based flame retardants with inorganic-based flame retardants such as phosphorus-based flame retardants and metal hydroxides.
As such phosphorus-based flame retardant, phosphoric ester-based flame retardants of resorcinol derivatives and bisphenol A derivatives are known, and these are used in polycarbonates and polyesters.
However, phosphoric ester-based flame retardants are in a liquid form or have a low melting point, and these flame retardants, when blended into a resin, exhibit plasticizing effect and deteriorate the physical properties of the resin. In addition, a blending device for liquid additives is required in order to blend such a phosphoric ester-based flame retardant into a resin.
As a process of solidifying a phosphoric ester-based flame retardant, Patent Document 1 proposes a process in which a solid flame retardant is obtained by allowing bis(2,6-dimethylphenyl)phosphoric chloride and resorcinol to react to produce a high-purity phosphoric ester. In Patent Documents 2 and 3, it is proposed to produce a solid flame retardant by applying stress load and using a seed crystal.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H5-320205 (Claims, etc.)
Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. H10-504317 (Claims, etc.)
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2001-131339 (Claims and Examples)